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1 引言通常的硫化钠处理液和排放液成份复杂、色度深,其硫离子测定采用一般的氧化法、比色法和直接电位法很难满足快速、准确、方便的要求。用硫电极作指示电极,Ag~+、Pb~(2+)、Cd~(2+)作滴定剂直接电位滴定的报道不少,但在硫化物抗氧化缓冲(SAOB)溶液中,Ag~+与其溶液中抗坏血酸发生氧化还原反应;Pb~(2+)、Cd~(2+)滴定终点电位突跃小,均不能满足测定要求。Hg~(2+)对硫电极能产生超Nernst响应,并且HgS沉淀非常稳定(K_(SP)=10~(-50)),用Hg~(2+)作滴定剂具有滴定电位稳定,终点电位突跃大的特点。但是Hg~(2+)与抗坏血酸发生氧化还原反应,所以此法在SAOB溶液中直接滴定受到限制。我们利用Hg~(2+)电位滴定的特点,采用Hg~(2+)-半胱胺酸(CySH)络离子作滴定剂,有效地降低了Hg~(2+)的氧化电位,使其在SAOB溶液中可直接电位滴定测定硫离子。2 实验部分2.1 主要仪器和试剂 PXJ-1型数字式离子计;217型双液接饱和甘汞电极;自制硫电极;喷泡式吸收器:基准Hg~(2+)溶液(3.119×10~(-3)mol/L,0.6755g氧化汞,5ml浓硝酸,用水稀释至1L);Hg~(2+)-CySH标准溶液(6.238×10~(-4)mol/L,100ml基准Hg~(2+)溶液,0.5gCySH,用水稀释至500ml);测定底液(0.25mol/L抗坏血酸,1mol/L氢氧化钠,0.01mol/L EDTA-Na).
1 Introduction Common sodium sulfide solution and discharge liquid composition is complex, deep color, the determination of sulfur ions using the general oxidation method, colorimetry and direct potential method is difficult to meet the requirements of rapid, accurate and convenient. There are a lot of reports on direct potentiometric titration of Ag +, Pb 2+ and Cd 2+ using sulfur electrode as indicator electrode. However, in SAOB solution, Ag ~ + And its solution ascorbic acid oxidation and reduction reaction; Pb ~ (2 +), Cd ~ (2 +) titration end potential jump is small, can not meet the determination requirements. Hg 2+ could produce super-Nernst response to the sulfur electrode and the HgS precipitation was very stable (K_ (SP) = 10 ~ (-50)). Hg 2+ as a titrant had stable titration potential, Potential sudden jump characteristics. However, Hg 2+ reacts with ascorbic acid to cause redox reaction, so this method is limited by direct titration in SAOB solution. Using the characteristic of Hg 2+ potentiometric titration, we used Hg 2+ (2 +) - cysteine (CySH) complex as a titrant to effectively reduce the oxidation potential of Hg 2+ Sulfur ions can be directly potentiometric titrated in SAOB solution. 2 Experimental 2.1 Main Equipment and Reagents PXJ-1 digital ion meter; 217 double-liquid saturated calomel electrode; self-made sulfur electrode; bubble jet absorber: reference Hg 2+ solution (3.119 × 10 ~ (-3) mol / L, 0.6755g mercuric oxide, 5ml concentrated nitric acid and dilute to 1L with water); Hg 2+ - CySH standard solution (6.238 × 10 -4 mol / L) (2+) solution, 0.5 g CySH, diluted with water to 500 ml); assay substrate (0.25 mol / L ascorbic acid, 1 mol / L sodium hydroxide, 0.01 mol / L EDTA-Na).